Screening methods are needed to predict the risk of developing colon cancer. Those identified to be at high risk for developing colon cancer would be more motivated to make appropriate dietary changes. Recent research suggests that colon cancer patients are more likely to excrete breath methane than healthy control subjects. The overall objective of the proposed research is to look at breath methane excretion in a large group of subjects on low and high fiber diets. Two groups of subjects will be studied, those on low fiber diets and those consuming diets containing the 30 to 40 grams of dietary fiber recommended by the National Cancer Institute. Dietary fiber, protein, stool weight, transit time, frequency of defecation, and stool pH will be measured for all subjects. A multiple regressioin analysis will be run to determine the best predictors of breath methane excretion. In a follow-up study, the subjects consuming low fiber diets in the initial study will be given 25 grams of dietary fiber as wheat bran and the same parameters will be measured as in part 1. The proposed studies should determine what parameters are the best predictors of breath methane production. Also, breath methane will be measured repeatedly in a large number of subjects on low and higher fiber diets. We should have good data whether breath methane changes with diet or over time.